Heretofore, lithium intercalation compounds such as Li.sub.1+X Mn.sub.2-X O.sub.4+Y have been used in positive electrodes for 4 V secondary lithium and lithium ion batteries. The spinel LiMn.sub.2 O.sub.4 intercalation compound was first obtained by Wickham and Croft by heating lithium carbonate and manganese oxide in a 1:2 lithium to manganese molar ratio. D. G. Wickham and W. J. Croft, Crystallographic and Magnetic Properties of Several Spinels Containing Trivalent JA-1044 Manganese; J. Phys. Chem. Solids 7, 351-360 (1958). As demonstrated in U.S. Pat. No. 4,426,253 to Hunter, the acid treatment of LiMn.sub.2 O.sub.4 forms a .lambda.-MnO.sub.2 which can be used in a positive electrode for electrochemical power sources. It was later discovered that the spinel LiMn.sub.2 O.sub.4 could be used as the positive electrode for a secondary lithium cell. Thackery et al., Lithium Insertion Into Manganese Spinels; Material Research Bulletin 18, 461-472 (1983).
The mean particle size and the particle size distribution are two of the basic properties characterizing the positive electrode intercalation materials for secondary lithium batteries. These properties are considered to be important because they directly influence the charge-discharge rate capability, the safety cell performance, the electrode formulation and the electrode coating process of positive electrodes containing these materials. In addition, a decrease in the mean particle size and distribution of the intercalation compounds typically results in an increase in the cycleability of these compounds. The reason for the increase in cycleability is that smaller particles are relatively more flexible than larger particles and therefore the changes in the crystal lattice parameters which occur during cycling do not damage the cycleability of the smaller particles to the degree that the larger particles are damaged.
Nevertheless, a decrease in the mean particle size results in a significant increase in the electronic resistivity of the spinel compounds. The electronic resistivity is controlled by the contact resistivity between the particles which rises significantly due to an increase in the number of contact boundaries which the electrons have to overcome. The increase in electronic resistivity leads to an increase in the electrode polarization which decreases both the specific capacity and charge-discharge rate capability of the electrode. Furthermore, a decrease in the particle size is generally coupled with an unwanted decrease in the tapped or powder density. Because many batteries such as batteries for electronics have fixed volumes, it is preferred that the spinel material used in the positive electrode of these batteries has a high tapped density, so there is essentially more chargeable material in the positive electrode. A higher tapped density results in a positive electrode having a higher overall capacity. Therefore, depending on the nature of the intercalation compounds and the electrode formulation, the cycleability, specific capacity, tapped density and charge-discharge rate of the spinel material should be considered in determining a desirable particle distribution for the spinel material.
Accordingly, these factors have been considered in the preparation of LiCoO.sub.2 intercalation compounds, where the desired particle size has been achieved by grinding the LiCoO.sub.2 material. Nevertheless, grinding Li.sub.1+X Mn.sub.2-X O.sub.4+Y intercalation compounds results in a considerable reduction in specific capacity. V. Manev et al., Rechargeable Lithium Battery With Spinel-Related .lambda.-MnO.sub.2. Part III. Scaling-up Problems Associated With LiMn.sub.2 O.sub.4 Synthesis, J. Power Sources 54, 323-328 (1995). As described in this article, the reduction in specific capacity is due to changes in the Li.sub.1+X Mn.sub.2-X O.sub.4+Y structure which occur as a result of the stress of mechanical treatment, measured by the contraction of the crystal lattice parameter a. Therefore, grinding the Li.sub.1+X Mn.sub.2-X O.sub.4+Y material is not a desirable method of reducing the mean particle size and particle size distribution of spinel Li.sub.1+X Mn.sub.2-X O.sub.4+Y intercalation compounds.